1. Field of the Invention
Exemplary embodiments of the present invention relate to a sheet adjusting device for adjusting a sheet to a given position on a sheet setting plate, a sheet holding receptacle including the sheet adjusting device, and an image forming mechanism including the same.
2. Description of the Related Art
Known related-art apparatuses that handle sheet-like recording media such as image forming apparatuses (copiers and printers), image reading apparatuses (scanners), and automatic document feeders (ADFs) have a sheet adjusting device for adjusting a sheet such as a recording sheet including an OHP (overhead projector) film, and a document sheet, to a given position in a direction perpendicular to a sheet conveyance direction on a sheet setting portion. For example, related-art image forming apparatuses include a sheet adjusting device in each sheet cassette or on each manual feed tray for holding recording sheets. Further, the scanners and the ADFs are also known to include such a sheet adjusting device on a document setting table on which original document sheets are placed.
Typically, in related-art sheet adjusting devices, regulating member regulates the sheet member placed on a sheet setting plate or a document setting table to adjust the position of the sheet member. For example, a sheet adjusting device provided to an image forming apparatus described in Japanese Patent Application Publication No. 07-267474 (JP-H07-267474-A) includes two side fences as regulating members for slidably moving on the sheet setting plate in a direction perpendicular to the sheet conveyance direction. These two side fences, at rest at their home position, are spaced apart so that a space wider than a recording sheet can be formed therebetween.
When a sheet is set on the sheet setting plate or the document setting table of the sheet adjusting device, the two side fences are retracted to their home positions. Under this condition, if an operator sets a stack of recording sheets between the two fences and transmits a command to drive the side fences, a drive unit starts to move the two side fences slidably toward the center the sheet setting plate. The two side fences slide and contact either side of the recording sheet misaligned to one side in a direction perpendicular to the sheet conveyance direction, so as to move the misaligned recording sheet slidably toward the center position of the sheet setting plate.
However, the related-art sheet adjusting devices can cause jam and skew when feeding a recording sheet that is positioned at the center of the sheet setting plate. Specifically, the two side fences slidably move from the respective home positions toward the center portion of the sheet setting plate for adjusting the position of the recording sheet loaded thereon, and stop moving after a period of time according to a sheet size designated by an operator has elapsed. By stopping at this position, the two side fences can form a space that is substantially the same as the sheet size. However, the actual size of a recording sheet can differ substantially from the theoretical size of a recording sheet due to stretching or shrinking of the sheet caused by changes in temperature and/or humidity and size error in processing.
Ideally, the sheet should lie flat on the sheet setting plate. However, when the actual size of a recording sheet placed on the sheet setting plate is greater than the theoretical size, the recording sheet is forced into a smaller space formed between the side fences, which can bend the recording sheet upward at the center portion of the surface of the recording sheet in a direction perpendicular to the sheet conveyance direction. The recording sheet can be transported from the sheet setting plate with the surface bent upward, which can easily cause paper jams.
Conversely, when the actual size of a recording sheet placed on the sheet setting plate thereof is smaller than the theoretical size; a gap is formed between the recording sheet and at least one of the side fences. With such a gap, the position of the recording sheet cannot be adjusted along the sheet conveyance direction and can be left misaligned. Accordingly, by feeding the slanted recording sheet from the sheet setting plate, skew can be caused in sheet transportation.
The problems described above can happen not only in the sheet adjusting device provided to the image forming apparatus but also in a sheet adjusting device provided to an ADF, scanner, and post-processing apparatus for aligning, stapling, and so forth.